These instructions are intended for those with little H/W construction experience. They are basically a description of how I assembled my prototypes. Those of you who have more experience will no doubt favor your own approach. In either case I hope these help.
The first thing to do is locate all the components. I have tried in the parts list to give Radio Shack part numbers where possible. The only part you might have trouble locating is the MOSTEK I.C. This is not exactly a mass marketed item though they (MOSTEK) might not like to hear me say so. In any event, locate this chip first and until you do don't spend your money on the remaining components. When you do get it, remember to leave it in it's anti-static protection until you are ready to install it in the board.
The small circuit board from Radio Shack makes assembly easier and neater than the alternatives. Don't be tempted to save money by scrimping on the socket for the chip, it's worth it's weight in gold.
Start with the socket, installing it in the middle of the board. Bend two legs at opposite corners of the socket over to lock the socket into the board and prevent it falling out as you manipulate the remaining components into place. Now plan the position of the remaining components around the board. Sketck out the layout if you like, it's better to delay now then to have to unsolder everything later because you can't fit that last component. The crystal should be mounted flat rather than standing up to take up less room in the case. Take care if the crystal casing is not insulated, to avoid shorting to any other component leads etc. Wrap it with a layer of tape if you like.
Next mount the capacitors and resistors, remembering to bend the leads over a little to hold them in place until you solder them. Check your work regularly to ensure you match the schematic. It's real easy to miss a ground connection or whatever and like we said, it's better to find any errors now
before
soldering. Once you're happy with the layout and the construction solder the components in, take your time and try to keep the iron in contact with the components as short a time as possible. Fortunately these components aren't too sensitive to heat (except the crystal) and should give you no trouble. Don't apply too much solder, it tends to blob easily on this board and can bridge between traces easily. Now trim the leads close to the board with a side cutters and check for solder blobs and shorts. If you find any bridges between pads you can often remove them by running the tip of the iron along the gap between the traces. The solder won't stick to the board and will tend to flow back onto the traces.
Now is a good time to check out the board with a meter if you have one, to verify the circuit is wired right. If you have no meter check each path carefully by eye.
This done, the next step is to solder the connecting wires into place. I used ribbon cable for the interconnect between the board and the D-connector. Be
careful with the wiring at this stage as you can do damage to your 64/128 by miswiring. Label the conductors of the cable or note down the colors and the pin numbers you intend to assign them to. The connector housing should be left till last, so you can verify the wiring with a meter. The length of wire between the board and connector is up to you. I used about 8 inches. This allows the RTC to sit in it's box atop my 128, just over the logo plate. It may not look pretty but I wouldn't use GEOS without it. The batteries should be wired also, again take care with the polarity and ensure that you have the diode around the right way. Check the wiring again now.
When all is complete, insert the chip. Take care to ground yourself and the board before
When all is complete, insert the chip. Take care to ground yourself and the board before removing the chip from the anti-static foam and hold the chip by the ends, try not to touch the leads. You'll probably have to straighten the legs of the chip to fit them into the socket. Power up with the batteries and check the current drawn with a meter if you have one. It should be about 1mA. Much more (I mean a
more) implies either unstable oscillation of the crystal, and/or a short somewhere. If so, one tip is to cut the traces of the board that connect with the crystal to the minimum length required. That is remove any 'antennaes' that could be causing the oscillation. When my prototype oscillated it was because the trimming capacitor was adjusted way off, so if you use a trimmer, power down, adjust the trimmer and apply power again. The current draw when my prototypes were in oscillation reached 1Amp briefly. I was sure this would fry the chip but it survived, just got VERY hot.
If you have no meter, power up and feel the chip. If it gets warm or hot power down and look for the problem. Oh and make sure that your batteries are OK. You might want to use regular batteris for these tests as they won't supply as much current and might save your chip from destruction.
IF all is well now, remove the batteries, turn off your computer and plug the unit into the joystick port (#2). Turn on the computer and make sure it comes up okay. If not power down immediately and llocate the problem, don't try to debug the problem with the power on. Hopefully everything is okay to this point and the computer shows no ill affects from the experience. If so, boot GEOS and proceed as I describe in the document file. I hope it performs smoothly for you. If not, and you're lost as to why, feel free to contact me on Q-Link and I'll try to help.
The tools I recommend you have to build the RTC are:
(.txt)